PROJECT SUMMARY Insects use of multiple developmental and physiological means to limit the impact of adverse climate and environments. One key strategy used by many insects in temperate environments, including important mosquito vector species, is seasonal diapause. This behavior is marked by developmental arrest throughout the winter period, often triggered by photoperiod to initiate diapause preparation. The mechanics of how insects in general and mosquito vectors specifically measure this photoperiod to initiate this behavior remains underexplored. This project seeks to characterize the genetic underpinnings of diapause behavior in the mosquito species Aedes albopictus induced by light sensation and photoperiodicity. We seek to understand specifically what elements of the visual system are implicated in the measurement of day length. The recent expansion in gene editing technologies enabled by CRISPR-Cas9- mediated transgenesis form the keystone of this proposal. We will produce a variety of laboratory-maintained mosquito lines deficient in distinct aspects of light detection to assay Aedes albopictus?s ability to prepare for, enter, and exit diapause when reared with appropriate token stimuli. Additionally, this proposal requires increased understanding of visual physiology of this mosquito species, particularly in light of our recent work demonstrating visual system differences between the mosquito Aedes aegypti and the well- studied Drosophila melanogaster. This proposal will address areas neglected in previous diapause research utilizing modern technologies and will set groundwork for future work both in diapause and generally on the mosquito visual system. The identification of the roles of genes involved in developmental and life history decisions show promise for producing new targets for mosquito control and gene drive technologies. This effort may identify possibilities for development-targeting control strategies.